{"abstract":"Additional-dwelling purchases under 250000 pay no surcharge.","category":"Tax bracket computation","checks":6,"contract":"solve(price, ftb, additional, nonresident): stipulated property transfer tax in whole pounds. Normal slices: 0% to 250000, 5% to 925000, 10% to 1500000, 12% above. First-time-buyer slices (0% to 425000, 5% to 625000) apply only when ftb is true, the purchase is not an additional dwelling, and price <= 625000; otherwise normal slices. Surcharges add percentage points to every slice including 0% slices: +3 for an additional dwelling when price >= 40000, +2 for a non-resident buyer; they stack. Return the tax rounded down to whole pounds.","contract_signature":"price, ftb, additional, nonresident","evaluation_group":"w2-tax_bracket_computation-property-transfer-slices","failed_approach":"Surcharging zero slices only for additional dwellings still exempts non-resident buyers' zero slice.","family":"w2-tax_bracket_computation-property-transfer-slices-surcharge-zero-slice","id":"FA-62601","implementations":{"attempt":{"sha256":"3e816a7353ac2dd4db06b0eb67b2552ff47cb6ef552c6d5c5ba4e0a4bf176b18","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(price, ftb, additional, nonresident):\n    normal = [(250000, 0), (925000, 5), (1500000, 10), (None, 12)]\n    first = [(425000, 0), (625000, 5)]\n    use_ftb = ftb and not additional and price <= 625000\n    bands = first if use_ftb else normal\n    sur = (3 if additional and price >= 40000 else 0) + (2 if nonresident else 0)\n    tax, lower = 0, 0\n    for upper, rate in bands:\n        top = price if upper is None else min(price, upper)\n        if top > lower: tax += (top - lower) * ((rate + sur) if rate else (3 if additional and price >= 40000 else 0))\n        if upper is None or price <= upper: break\n        lower = upper\n    return tax // 100\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncases = [[('regression surcharge-zero-slice 1', (300000, False, True, True), 17500),\n  ('regression surcharge-zero-slice 2', (39999, False, False, True), 799),\n  ('control: normal', (300000, False, False, False), 2500),\n  ('control: first-time buyer', (500000, True, False, False), 3750),\n  ('control: ftb at cap', (625000, True, False, False), 10000),\n  ('control: ftb over cap', (625001, True, False, False), 18750)],\n [('regression surcharge-zero-slice 1', (300000, False, True, False), 11500),\n  ('regression surcharge-zero-slice 2', (400000, True, True, False), 19500),\n  ('partial repair guard 1', (625000, False, True, True), 50000),\n  ('partial repair guard 2', (40000, False, False, True), 800),\n  ('control: ftb over cap', (625001, True, False, False), 18750),\n  ('control: additional nonresident', (300000, False, True, True), 17500),\n  ('control: below surcharge floor', (39999, False, True, False), 0),\n  ('control: nonresident cheap', (39999, False, False, True), 799)],\n [('regression surcharge-zero-slice 1', (625000, False, True, True), 50000),\n  ('regression surcharge-zero-slice 2', (40000, False, True, False), 1200),\n  ('partial repair guard 1', (250001, True, False, True), 5000),\n  ('partial repair guard 2', (628677, True, True, True), 50367),\n  ('control: below surcharge floor', (39999, False, True, False), 0),\n  ('control: nonresident cheap', (39999, False, False, True), 799),\n  ('control: ftb additional', (400000, True, True, False), 19500),\n  ('control: expensive', (2000000, False, False, False), 151250)],\n [('regression surcharge-zero-slice 1', (40000, False, False, True), 800),\n  ('regression surcharge-zero-slice 2', (625001, True, True, False), 37500),\n  ('partial repair guard 1', (250001, False, True, True), 12500),\n  ('partial repair guard 2', (625001, False, False, True), 31250),\n  ('control: expensive', (2000000, False, False, False), 151250),\n  ('control: odd pounds', (250013, False, False, False), 0), ('control: normal', (300000, False, False, False), 2500),\n  ('control: first-time buyer', (500000, True, False, False), 3750)],\n [('regression surcharge-zero-slice 1', (925000, False, True, False), 61500),\n  ('regression surcharge-zero-slice 2', (919321, True, True, False), 61045),\n  ('partial repair guard 1', (250001, False, False, True), 5000),\n  ('partial repair guard 2', (2021858, False, False, True), 194310),\n  ('control: first-time buyer', (500000, True, False, False), 3750),\n  ('control: ftb at cap', (625000, True, False, False), 10000),\n  ('control: ftb over cap', (625001, True, False, False), 18750),\n  ('control: additional dwelling', (300000, False, True, False), 11500)]]\nfor label, args, expected in cases[N - 1]:\n    check(label, solve(*args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"f6e78966a5facf4ef0ecabf40c6f28c028dd66907c9b775117d1bd461d1b8b0d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(price, ftb, additional, nonresident):\n    normal = [(250000, 0), (925000, 5), (1500000, 10), (None, 12)]\n    first = [(425000, 0), (625000, 5)]\n    use_ftb = ftb and not additional and price <= 625000\n    bands = first if use_ftb else normal\n    sur = (3 if additional and price >= 40000 else 0) + (2 if nonresident else 0)\n    tax, lower = 0, 0\n    for upper, rate in bands:\n        top = price if upper is None else min(price, upper)\n        if top > lower: tax += (top - lower) * ((rate + sur) if rate else 0)\n        if upper is None or price <= upper: break\n        lower = upper\n    return tax // 100\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncases = [[('regression surcharge-zero-slice 1', (300000, False, True, True), 17500),\n  ('regression surcharge-zero-slice 2', (39999, False, False, True), 799),\n  ('control: normal', (300000, False, False, False), 2500),\n  ('control: first-time buyer', (500000, True, False, False), 3750),\n  ('control: ftb at cap', (625000, True, False, False), 10000),\n  ('control: ftb over cap', (625001, True, False, False), 18750)],\n [('regression surcharge-zero-slice 1', (300000, False, True, False), 11500),\n  ('regression surcharge-zero-slice 2', (400000, True, True, False), 19500),\n  ('partial repair guard 1', (625000, False, True, True), 50000),\n  ('partial repair guard 2', (40000, False, False, True), 800),\n  ('control: ftb over cap', (625001, True, False, False), 18750),\n  ('control: additional nonresident', (300000, False, True, True), 17500),\n  ('control: below surcharge floor', (39999, False, True, False), 0),\n  ('control: nonresident cheap', (39999, False, False, True), 799)],\n [('regression surcharge-zero-slice 1', (625000, False, True, True), 50000),\n  ('regression surcharge-zero-slice 2', (40000, False, True, False), 1200),\n  ('partial repair guard 1', (250001, True, False, True), 5000),\n  ('partial repair guard 2', (628677, True, True, True), 50367),\n  ('control: below surcharge floor', (39999, False, True, False), 0),\n  ('control: nonresident cheap', (39999, False, False, True), 799),\n  ('control: ftb additional', (400000, True, True, False), 19500),\n  ('control: expensive', (2000000, False, False, False), 151250)],\n [('regression surcharge-zero-slice 1', (40000, False, False, True), 800),\n  ('regression surcharge-zero-slice 2', (625001, True, True, False), 37500),\n  ('partial repair guard 1', (250001, False, True, True), 12500),\n  ('partial repair guard 2', (625001, False, False, True), 31250),\n  ('control: expensive', (2000000, False, False, False), 151250),\n  ('control: odd pounds', (250013, False, False, False), 0), ('control: normal', (300000, False, False, False), 2500),\n  ('control: first-time buyer', (500000, True, False, False), 3750)],\n [('regression surcharge-zero-slice 1', (925000, False, True, False), 61500),\n  ('regression surcharge-zero-slice 2', (919321, True, True, False), 61045),\n  ('partial repair guard 1', (250001, False, False, True), 5000),\n  ('partial repair guard 2', (2021858, False, False, True), 194310),\n  ('control: first-time buyer', (500000, True, False, False), 3750),\n  ('control: ftb at cap', (625000, True, False, False), 10000),\n  ('control: ftb over cap', (625001, True, False, False), 18750),\n  ('control: additional dwelling', (300000, False, True, False), 11500)]]\nfor label, args, expected in cases[N - 1]:\n    check(label, solve(*args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"A deterministic, bounded teaching model with a stipulated toy contract; it makes no claim of conformance to any real regulation, standard, or institution's rules. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"w2-tax_bracket_computation-property-transfer-slices-surcharge-zero-slice","generated_at":"2026-09-29T14:47:06.049927+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Tax computations hinge on which slice, threshold, ordering and rounding rule applies at each step; a misplaced boundary silently misstates liabilities.","root_cause":"The surcharge is added only to slices with a positive base rate.","sha256":"d5139c426d2dc95d45e35f04612e103696be4cd269937ad210ba27867ce93ae3","title":"Surcharges are not charged on zero-rate slices · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":41.851,"exit_code":1,"observations":[{"actual":12500,"check":"regression surcharge-zero-slice 1","expected":17500,"passed":false},{"actual":0,"check":"regression surcharge-zero-slice 2","expected":799,"passed":false},{"actual":2500,"check":"control: normal","expected":2500,"passed":true},{"actual":3750,"check":"control: first-time buyer","expected":3750,"passed":true},{"actual":10000,"check":"control: ftb at cap","expected":10000,"passed":true},{"actual":18750,"check":"control: ftb over cap","expected":18750,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression surcharge-zero-slice 1\", \"actual\": 12500, \"expected\": 17500, \"passed\": false}, {\"check\": \"regression surcharge-zero-slice 2\", \"actual\": 0, \"expected\": 799, \"passed\": false}, {\"check\": \"control: normal\", \"actual\": 2500, \"expected\": 2500, \"passed\": true}, {\"check\": \"control: first-time buyer\", \"actual\": 3750, \"expected\": 3750, \"passed\": true}, {\"check\": \"control: ftb at cap\", \"actual\": 10000, \"expected\": 10000, \"passed\": true}, {\"check\": \"control: ftb over cap\", \"actual\": 18750, \"expected\": 18750, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":43.152,"exit_code":1,"observations":[{"actual":5000,"check":"regression surcharge-zero-slice 1","expected":17500,"passed":false},{"actual":0,"check":"regression surcharge-zero-slice 2","expected":799,"passed":false},{"actual":2500,"check":"control: normal","expected":2500,"passed":true},{"actual":3750,"check":"control: first-time buyer","expected":3750,"passed":true},{"actual":10000,"check":"control: ftb at cap","expected":10000,"passed":true},{"actual":18750,"check":"control: ftb over cap","expected":18750,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression surcharge-zero-slice 1\", \"actual\": 5000, \"expected\": 17500, \"passed\": false}, {\"check\": \"regression surcharge-zero-slice 2\", \"actual\": 0, \"expected\": 799, \"passed\": false}, {\"check\": \"control: normal\", \"actual\": 2500, \"expected\": 2500, \"passed\": true}, {\"check\": \"control: first-time buyer\", \"actual\": 3750, \"expected\": 3750, \"passed\": true}, {\"check\": \"control: ftb at cap\", \"actual\": 10000, \"expected\": 10000, \"passed\": true}, {\"check\": \"control: ftb over cap\", \"actual\": 18750, \"expected\": 18750, \"passed\": true}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}